1. Field of the Invention
The present invention relates to a gain controller for use in an apparatus comprising a frequency characteristic controller (hereinafter called tone controller) and, more particularly, to a gain controller of the type capable of controlling a gain in the apparatus by maintaining a good S/N ratio and preventing a clipping distortion from causing upon saturation in the tone controller.
2. Description of the Prior Art
Heretofore, an electronic volume control circuit has been used in an audio equipment such, for example, as it is shown in the disclosure of Japanese Laid-open Utility Model Application No. 63-92418 hereby incorporated as the prior art by reference. In such electronic volume control circuit, a first depression detection signal is fed to a control circuit when a first push button switch is depressed for controlling the electronic volume controller to increase a resistance value thereof and a second depression detection signal is fed to the control circuit when a second push button switch is depressed for controlling the electronic volume controller to decrease a resistance value thereof, thereby if the first and the second depression detection signals are fed simultaneously to the control circuit, the electronic volume controller is so adjusted as to be set to a certain amount of value under the control of the control circuit.
Further, the disclosure of Japanese Utility Model Publication No. 63-111015 is incorporated as the prior art tone control device for audio equipments by reference. In such tone control device, a tone characteristic for a reproduced sound is set by a tone quality setting unit and the selected tone qualities for respective sound sources are stored in a memory unit, the tone quality of an audio signal selected one out of several sound sources is controlled on the basis of the corresponding tone characteristic thereto by means of a tone controller, and the tone characteristic that corresponds to the selected sound source is read from the memory unit when the reproduction of the selected sound source is started and fed to the tone controller by means of a control unit.
FIG. 1 shows a schematic diagram of an audio equipment comprising the prior art tone controller, wherein numeral 1 denotes a tone controller, numeral 6 denotes a fixed attenuator made up of fixed resistors and numeral 7 denotes a volume controller made up of a variable resistor.
The tone controller 1 is provided for changing a frequency characteristic by setting a gain and an attenuation against a specific frequency band, thereby a frequency spectrum of an audio signal can be varied.
On the other hand, the volume controller 7 is provided for attenuating the audio signal uniformly across the whole band by a discretionary amount of level.
The operation of the prior art will now be described more in detail, if the frequency characteristic of the tone controller 1 is so set as to be "0" dB gain within a lower frequency band A and "a" dB gain within a higher frequency band B, relative gains in the frequency characteristic of the audio signal at input points between blocks will be shown in FIGS. 2a-2c. Firstly, a level of an input signal "i" to the fixed attenuator 6 of FIG. 1 is set to "0" dB as it is shown in FIG. 2a and this level is assumed to be an allowable amplitude for the tone controller 1. The level of an output signal "ii" of the fixed attenuator 6 is attenuated by an amount of "b" dB in the whole frequency band as it is shown in FIG. 2b. Accordingly, there needed is the setting of the maximum input level in advance against the tone controller 1 in consideration of the maximum boosting (the maximum gain) value thereof.
In other words, it is necessary that the attenuation of "b" dB that conforms to a margin should be allocated within the allowable input value for the tone controller 1. Therefore, the amount of margin "b" dB is so selected as to be such a value within which a voice signal is not clipped even at the maximum boosting in the tone controller 1. Then an output boosted by the amount of "a" dB at the higher frequency band B is attained from the tone controller 1 as it is shown in FIG. 2c.
As it has been described above, in the audio equipment comprising the prior art tone controller, the margin provided for the tone controller will be of no use if there is no boosting in the tone controller and resulting in the attenuation of the audio signal level less than required signal level. This, in turn, aggravates the S/N ratio and deteriorates the quality of the audio signal.
It is therefore an object of this invention to eliminate the problems as described above and to provide a gain controller comprising a tone controller from which an audio signal secured of good S/N ratio is derived in all the time regardless of an amount of boosting such as of no boosting as well as of small amount of boosting therein.